In electronic fuel injection systems for internal combustion engines both manifold absolute pressure and atmospheric pressure, inter alia, are required by the system logic in calculating the proper injector open time for effective and efficient engine operation. Accordingly, one pressure sensor or transducer is provided in the engine manifold to sense manifold absolute pressure and generate a signal proportional thereto and a second sensor or transducer is provided to sense atmospheric pressure and generate a signal proportional thereto.
Since pressure sensors are relatively expensive, means for using a single pressure sensor to sense both manifold absolute pressure and absolute pressure have been devised. One such means has involved the use of solenoid valves disposed between each pressure region to be measured and a pressure sensor so that the pressure sensor can be time shared. Another means has involved the use of a differential pressure switch connected across the engine manifold and the atmosphere and arranged so that switch over occurs at a predetermined pressure differential. A pressure sensor is provided to sense the manifold absolute pressure. Upon switch over the signal from the manifold absolute pressure sensor is sampled and the offset added to the sampled signal to provide a signal related to absolute pressure.